The structure of protein that is unaffected by heating is :

Primary structure of proteins: Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that is said to be the primary structure of that protein.

Secondary structure of proteins: The secondary structure of protein refers to the shape in which a long polypeptide chain can exist.

Tertiary structure of proteins: The tertiary structure of proteins represents overall folding of the polypeptide chains i.e., further folding of the secondary structure.

Quaternary structure of proteins: Some proteins are composed of two or more polypeptide chains referred to as subunits. The spatial arrangement of these subunits with respect to each other is known as quaternary structure.

During denaturation Quaternary, secondary and tertiary structures are destroyed, but primary structure remains intact.